Power plant

ABSTRACT

A power plant ( 10 ) having a primary water-steam cycle ( 11 ) that generates a primary electrical load via a generator ( 101 ) and a recovery cycle ( 12 ) that generates a secondary electrical load via a generator ( 102 ). The overlap between the cycles ( 11, 12 ) occurs in the condensing section ( 40 ). An evaporator ( 45 ) transfers heat from the exhaust line ( 41 ) of the primary cycle  11 ) to the conveying line ( 44 ) of the recovery cycle ( 12 ).

RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/238,357 filed on Aug. 31, 2009. The entire disclosure of this application is hereby incorporated by reference. To the extent that inconsistencies may occur between the present application and the incorporated application, the present application governs interpretation to the extent necessary to avoid indefiniteness and/or clarity issues.

BACKGROUND

A power plant converts fuel (e.g., coal, oil, nuclear, etc.) into electrical kilowatts via a closed steam cycle. In a typical cycle, feedwater is superheated into high pressure steam, and then routed to the high pressure (HP) turbine. The steam exiting the HP turbine can be reheated and then passed (as superheated steam) through the intermediate pressure (IP) turbine. From the IP turbine the steam passes to the low pressure (LP) turbine whereat it becomes saturated steam. The steam exits LP turbine into a condenser whereat it is condensed into liquid, pumped through cascading heaters, and returned to the boiler to repeat the cycle. Conventional wisdom suggests that the lower the outlet pressure of the LP turbine, the more efficient the conversion and the better the heat rate.

SUMMARY

A power plant is provided wherein the condensing section is constructed to convert heat into usable electricity via a secondary generator. This results in optimum power plant operation going completely against the traditional approach of constantly striving to reduce LP-turbine-exhaust pressure in the interest of efficiency. The water-steam cycle is purposely operated to provide a high LP-outlet pressure (e.g., at or above 5 psia and more preferably above 15 psia) to capitalize on the heat expelled during condensation. Instead of this heat being lost to a lake or a cooling tower, it serves as the heat source for separate heatpump system.

DRAWINGS

FIG. 1 is a schematic diagram of a power plant.

FIG. 2 is a schematic diagram of the condensing section of the power plant.

DESCRIPTION

Referring now to the drawings, and initially to FIG. 1, a power plant 10 is schematically shown. The power plant 10 incorporates a water-steam cycle 11 used to generate a primary amount of electricity. The plant 10 also incorporates a refrigerant recovery cycle 12 used to generate electricity from the heat normally expelled during condensation.

In the primary cycle 11, feedwater is superheated in a boiler 21. The superheated high pressure steam flows to the HP turbine 31 and the HP-turbine-exhaust steam is reheated in boiler 22 (which may be part of the same furnace structure as the superheater boiler 21). The reheated steam passes to the inlet of the IP turbine 32. The exhaust steam from the IP turbine 32 (usually still superheated steam) then enters the LP turbine 33 whereat it becomes wet steam. The wet steam leaving the LP turbine flows to the condensing section 40 (via line 41) whereat it is condensed into liquid water.

The condensate flows to the suction side of the hotwell pump 51 (via line 42) whereat it is pumped through heaters 61-64. The heaters 61-64 have crossflows supplied by extracted steam from descending stages of the LP turbine 33. The crossflow drains of the heaters 61-64 cascade to the upstream heater, with the first heater 61 draining into the condensate section 40 (via line 43).

The condensate exiting the heater 64 is delivered to the dearator 71 and thereafter to the suction side of the boiler-feed-water pump 81. The pump 81 pushes the feedwater through the heaters 91-92 and back to the boiler 21. The heater 91 has a crossflow supply extracted from the IP turbine 32 and a crossflow drain to the dearator 71. The heater 92 has a crossflow supply extracted from the HP turbine 31 and a crossflow drain to the heater 91.

When the exiting feedwater from the last heater 92 is returned to the superheater boiler 21, the cycle is repeated.

Referring now to FIG. 2, the condensing section 40 is shown in more detail. The condensing section 40 incorporates part of the primary water-steam cycle 11 (e.g., lines 41-43 pass through this section). The condensing section 40 also encompasses the refrigerant recovery cycle 12, which absorbs heat expelled by line 41 as wet steam from the LP turbine exhaust is condensed into liquid.

The recovery cycle 12 includes a refrigerant line 44 carrying a fluid that can be evaporated within the expected temperature range of the wet steam exiting the LP turbine 33. In most instances, this will be greater than 160° F., greater than 180° F., greater than 200° F. and/or greater than 220° F. As is explained in more detail below, the primary cycle 10 is purposely operated so as to have a higher LP exhaust pressure and thus (because the steam is wet at this stage) a higher temperature.

The recovery cycle 12 further comprises an evaporator 45 that places the recovery line 44 in heat-transfer relationship with exhaust line 41 from the LP turbine 33. A turbine 46 is situated downstream of the evaporator 45, a compressor 47 is situated downstream of the turbine 46, and a condenser 48 is situated downstream of the evaporator and an expander 49 is downstream of the condenser 48 (and upstream of the evaporator 45).

The turbine string 31-33 of the primary cycle 11 is operably coupled to a generator 101 which produces the primary electrical output of the power plant 10 (e.g., more than 10 MW, more than 500 MW, more than 1000 MW, more than 1100 MW, more than 1300 MW, etc.) The turbine 46 of the recovery cycle 12 is operably coupled to a generator 102. While the electricity generation of the generator 102 may be significantly less than that of generator 101 (e.g., less than 10%, less than 5% and/or less than 2% of that generated by generator 101), this electricity is produced from heat conventionally lost in the condensation section.

The advantages of incorporating the recovery cycle 12 into a power plant are perhaps best explained by establishing a baseline back to conventional operation for comparison. In a traditional power-plant cycle, optimum performance is believed to occur at a condenser pressure of about 2.5 psia, which corresponds to a saturation temperature of about 100° F. and an enthalpy of about 1100 Btu/lb. Assume for the purposes of comparison that the power plant (when conventionally operated) has a respectable heat rate of 10,000 Btu/Kw and 1300 MW are when 1000 psig superheated steam is supplied to the HP turbine 31 at a rate of 14 MMlb/hr. (This corresponds to a 13,000 MMBtu/hr being provided to the turbine string 31-33.)

If the heat of vaporization is approximated at 1000 Btu/hr, about 14,000 mM Btu/hr must be rejected in the condensation section for the LP exhaust steam to liquefy (i.e., 14 MM lb/hr/1000 Btu/hr). Assuming that the recovery cycle 12 is presumed to have coefficient of performance of 3 (which is not overly generous), about 4700 MM Btu/hr can be recovered and turned into about 470 MW of additional power by the generator 102.

With the power plant 10, optimum power plant operation may occur when parameters are adjusted to provide relatively high LP-outlet pressure (e.g., at or above 10 psia, 12 psia, 14 psia, 16 psia, 18 psia, 19 psia, etc.) to capitalize on the heat expelled during condensation. This is significantly greater than the LP-outlet pressures traditionally strived for in power-plant operation, specifically below 10 psia, below 5 psia, and/or about 2.5 psia (≈5″ mercury).

Such a purposely higher LP outlet enthalpy will most likely result a reduction of MW production by the primary cycle 10. For example, with an LP exhaust of 19 psia (about 1100 Btu/hr enthalpy) versus 2.5 psia (about 1150 Btu/hr enthalpy), about 700 mM Btu/hr (i.e., 50 Btu/lb*14 MMlb/hr) will not be converted by the primary cycle 10 into megawatts. Assuming a heat rate of 10,000 Btu/Kw, this translates into a loss 70 MW loss.

The MW loss suffered by the primary cycle 10 will usually be more than offset by that gained by the recovery cycle 12. For example, with a 70 MW loss by the primary cycle 10 and 470 MW gain by the recovery cycle 12, the net additional power is about 400 MW. This means that 1700 MW can now be produced for the same heat input, which reflects a heat rate of less than 7700 Btu/Kw (i.e., 13,000 MMBtu/hr/1700 MW). This corresponds to 23% improvement in heat rate, in an industry where 5% improvements are considered economically significant. Moreover, the condensing section 70 of the present invention substantially removes seasonal fluctuations (due to changing ambient temperatures) from the efficiency equation.

Although the power plant 10 and/or the condensing section 70 have been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In regard to the various functions performed by the above described elements (e.g., components, assemblies, systems, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. A power plant comprising: a primary water-steam cycle comprising a turbine operably coupled to a generator for generating a primary load of electricity, and an exhaust line from the turbine; and a recovery cycle comprising a turbine operably coupled to a generator for generating a secondary load of electricity, and a conveying line carrying a fluid passing through the turbine; wherein a condensing section incorporates part of the primary water-steam cycle and the recovery cycle; wherein the condensing section comprises an evaporator that transfers heat from the exhaust line of the primary cycle to the conveying line of the recovery cycle to evaporate the fluid upstream of the turbine.
 2. A power plant as set forth in claim 1, wherein the primary generator produces an electrical output load of more than 10 MW.
 3. A power plant as set forth in claim 2, wherein the primary generator produces an electrical output load of more than 500 MW.
 4. A power plant as set forth in claim 3, wherein the primary generator produces an electrical output load of more than 1000 MW.
 5. A power plant as set forth in claim 4, wherein the primary generator produces an electrical output load of 1300 MW or more.
 6. A power plant as set forth in claim 1, wherein the recovery generator produces an electrical output load that is 10% or less than that produced by the primary generator.
 7. A power plant as set forth in claim 6, wherein the recovery generator produces an electrical output load that is 8% or less than that produced by the primary generator.
 8. A power plant as set forth in claim 7, wherein the recovery generator produces an electrical output load that is 5% or less than that produced by the primary generator.
 9. A power plant as set forth in claim 8, wherein the recovery generator produces an electrical output load that is 2% or less than that produced by the primary generator.
 10. A power plant as set forth in claim 1, wherein the exhaust line of the primary cycle carries wet steam.
 11. A power plant as set forth in claim 10, wherein the fluid carried by the conveying line can be evaporated within the expected temperature range of wet steam in the exhaust line.
 12. A power plant as set forth in the claim 1, wherein the fluid carried by the conveying line can be evaporated at temperature less than 220° F.
 13. A power plant as set forth in claim 12, wherein the fluid carried by the conveying line can be evaporated at temperature less than 160° F.
 14. A power plant as set forth in claim 1, wherein the pressure within the exhaust line is greater than −1 psig.
 15. A power plant as set forth in claim 1, wherein the pressure within the exhaust line is about +5 psig or greater.
 16. A power plant as set forth in claim 1, wherein the turbine includes an HP turbine, an IP turbine, and an LP turbine, the exhaust line exhausting from the LP turbine.
 17. A power plant as set forth in claim 16, wherein the feedwater is superheated in the boiler into superheated steam upstream of the HP turbine.
 18. A power plant as set forth in claim 17, wherein the steam exhausting from the HP turbine is reheated in a boiler prior to entering the IP turbine.
 19. A power plant as set forth in claim 16, wherein the primary generator produces an electrical output load of more than 500 MW, wherein the recovery generator produces an electrical output load that is 10% or less than that produced by the primary generator, and wherein the pressure within the exhaust line is greater than −1 psig. 